The present invention is directed to call-switching equipment for telephone networks and in particular to devices for curbing abuse of direct-inward-access systems.
The combination of electronic, stored-program telephone switching systems with discounted bulk toll offerings gives rise to a feature that provides a convenient way to reduce telecommunications costs. In accordance with this feature, an authorized person at remote location can place a call to a "home office" private branch exchange (PBX), receive dial tone from the PBX, and place an outgoing call just as if he were calling from his office.
The industry uses the acronyms RSA (Remote Service Access) and DISA (Direct Inward Service Access) interchangeably to refer to this feature, to which we refer herein as DISA. DISA features are currently available primarily in conjunction with PBX systems, and we will accordingly refer to PBX systems for the purpose of concreteness. However, DISA-like features are also available to users of certain central-office-based services, and it will become apparent that the invention to be described below is applicable to these types of arrangements, too, as well as to a host of non-voice-based services, including but not limited to data networks and modem pools. The invention is equally powerful in providing protection of sensitive internal destinations, such as the maintenance ports of communications and computer systems.
DISA offers both cost and administrative advantages. If the firm that owns the PBX subscribes to bulk-rate toll services, such as WATS, placing a call through remote service access can reduce the cost of the call. For example, an employee whose home office is in Seattle but who has traveled to San Diego may want to call a customer in Fort Lauderdale. If he uses his telephone-company calling card, a ten-minute call at AT&T daytime rates may cost around $3.00. In contrast, his company may pay around $0.09 a minute on the average for both incoming and outgoing bulk services, so if the employee places the call instead to his Seattle office, which then switches it to the customer in Fort Lauderdale, the cost may be only about $1.80.
Moreover, the company's call-accounting system can thereby keep track of such calls automatically, relieving the company's accounting department of the need to allocate telephone costs manually among its various departments. In certain circumstances, it also provides a tool for measuring the performance of personnel whose jobs involve high levels of telephone activity.
Unfortunately, unscrupulous people can sometimes discover the passwords by which the DISA systems' owners attempt to restrict access to their facilities. Indeed, such occurrences have happened frequently, some of them resulting in large losses to the company that has availed itself of the DISA feature. In like manner, loss and system damage have resulted from fraudulent abuse of voice mail and messaging systems, to which the application of the invention is equally applicable.
Responses to this problem have been various. Some users have simply discontinued the DISA feature because of the risk of significant loss. Others have reconfigured to disable its use for calls to destination area codes known to be favorites of "hackers," and they may also monitor telephone traffic so as to identify unusual activity.
Of course, discontinuing the DISA service does eliminate the problem, but it also eliminates the savings that ordinarily result from DISA-service use. The other approaches can be fairly effective in general, but they lack flexibility, require excessive attention from the telecommunications manager, or both.